<html>
    <head>
        <meta>
    </head>
    <body>
        <script>
            var el = document.createElement('add-options');
            console.log(el);
            console.log(window.HTMLUnknownElement);
            console.log( window.HTMLElement);

            console.log(el.constructor === window.HTMLUnknownElement ||
                el.constructor === window.HTMLElement)
               console.log(   /HTMLUnknownElement/.test('HTMLUnknownElement')  ); 

        </script>
    </body>
</html>